Long-necked sauropods (SAHR-oh-pahdz) are the largest animals known to have walked on Earth. These giant plant-eating dinos include Apatosaurus and Brontosaurus. Their early relatives were big, too. Some, though, may have used a different strategy to get their girth, shows a new study.
Most early sauropod relatives shared a common suite of features. They had sturdy, pillarlike legs. They had elongated necks and forelimbs. And their bones grew continuously rather than in seasonal spurts. Scientists had considered this an essential blueprint for massive plant-eaters. But at least some ancient giants may have used a different strategy to get so big. That’s the conclusion of a new fossil analysis of sauropodomorphs (SAHR-oh-PAHD-oh-morfz). That group includes sauropods and some of their similarly shaped relatives.
Cecilia Apaldetti is a paleontologist. She works at the Universidad Nacional de San Juan in Argentina. She and her colleagues examined fossils of four early sauropodomorphs. One belonged to a newly identified species. The team named it Ingentia prima (Ihn-GEHN-tee-uh PREE-muh). The other three were an already known sauropodomorph called Lessemsaurus sauropoides (Lehs-ehm-SAHR-us sahr-uh-POY-deez). These “Lessemsauridae” (Lehs-ehm-SAHR-ih-day) date to the Late Triassic. That’s between 237 million and 201 million years ago. They were smaller than the later sauropods. But they were far from puny. The animals weighed in at an estimated 7 to 10 metric tons. That’s larger than an African elephant!
All four specimens showed a similar set of features. But they didn’t match sauropods and other sauropodomorphs. Instead of upright, pillarlike legs, the dinosaurs had crouched hind limbs. Their front limbs were flexed, with elbows splayed slightly outward. Growth patterns in the fossil bones suggest the animals grew in seasonal spurts rather than steadily. And when their bones grew, they did so unusually fast, Apaldetti says. The growth rate was “even higher than that of the giants that grew continuously.”
These features show there’s more than one way to build a giant dino, her team concludes. It published its findings online July 9 in Nature Ecology and Evolution.
I. prima and L. sauropoides shared some features with later sauropods, though. One was a respiratory system that appears similar to that of birds. The researchers found air sacs within the animals’ vertebrae. These sacs would have held large pockets of oxygen-rich air. They likely helped the dinos keep cool despite their large size. And they made the animals’ vertebrae lighter.
Martin Sander is a vertebrate paleontologist. He works at Universität-Bonn in Germany. He says I. prima presents the best evidence yet of this birdlike respiratory system in sauropodomorphs. Scientists previously weren’t sure. But he isn’t convinced that the Lessemsauridae show a distinct path to massive size. “For me, it’s more of an intermediate stage,” Sander says.
That sentiment is echoed by Jeffrey Wilson. He is a vertebrate paleontologist at the University of Michigan in Ann Arbor. He agrees that Lessemsauridae bone growth was cyclical. But the cycles weren’t necessarily seasonal, Wilson points out. There may have been long growth spurts with fewer lags. That could be a step toward the steady growth seen in sauropods, Wilson says.
The Lessemsauridae lived some 30 million years earlier than Jurassic sauropods, such as Brachiosaurus and Diplodocus. So their growth strategy came first, Apaldetti notes. But ultimately, the Jurassic giants “were more successful,” she says. They outweighed the sauropodomorphs by as much as 60 tons. And they outlived them by tens of millions of years.
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Apatosaurus A dinosaur whose name means deceptive lizard. It has a long neck and thick, whip-like tail. Formerly known as a brontosaurus, it lived during the Jurassic period, about 150 million years ago. In adulthood, this plant-eater would have weighed some 36 metric tons (40 short tons) and had an average length of perhaps 23 meters (75 feet). That would have made it one of the largest animals to ever roam the Earth.
birds Warm-blooded animals with wings that first showed up during the time of the dinosaurs. Birds are jacketed in feathers and produce young from the eggs they deposit in some sort of nest. Most birds fly, but throughout history there have been the occasional species that don’t.
colleague Someone who works with another; a co-worker or team member.
dinosaur A term that means terrible lizard. These ancient reptiles lived from about 250 million years ago to roughly 65 million years ago. All descended from egg-laying reptiles known as archosaurs. Their descendants eventually split into two lines. For many decades, they have been distinguished by their hips. The lizard-hipped line are believed to have led to the saurichians, such as two-footed theropods like T. rex and the lumbering four-footed Apatosaurus (once known as brontosaurus). A second line of so-called bird-hipped, or ornithischian dinosaurs, appears to have led to a widely differing group of animals that included the stegosaurs and duckbilled dinosaurs. But a new 2017 analysis now calls into question that characterization of relatedness based on hip shape.
ecology A branch of biology that deals with the relations of organisms to one another and to their physical surroundings. A scientist who works in this field is called an ecologist.
evolution (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed. Or the term can refer to changes that occur as some natural progression within the non-living world (such as computer chips evolving to smaller devices which operate at an ever faster speed).
forelimb The arms, wings, fins or legs in what might be thought of as the top half of the body. It’s the opposite of a hindlimb.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.
Jurassic Lasting from about 200 million to 145.5 million years ago, it’s the middle period of the Mesozoic Era. This was a time when dinosaurs were the dominant form of life on land.
limb (in physiology) An arm or leg. (in botany) A large structural part of a tree that branches out from the trunk.
online (n.) On the internet. (adj.) A term for what can be found or accessed on the internet.
oxygen A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).
paleontologist A scientist who specializes in studying fossils, the remains of ancient organisms.
respiratory Of or referring to parts of the body involved in breathing (called the respiratory system). It includes the lungs, nose, sinuses, throat and other large airways.
sauropod A very large, four-legged, plant-eating dinosaur with a long neck and tail, small head and massive limbs.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
vertebrate The group of animals with a brain, two eyes, and a stiff nerve cord or backbone running down the back. This group includes amphibians, reptiles, birds, mammals and most fish.